1. Field of the Invention
The present invention relates to a semiconductor apparatus, a semiconductor storage apparatus, a control signal generation method, and a replacing method, and particularly to a semiconductor apparatus, a semiconductor storage apparatus, a control signal generation method, and a replacing method including electric fuses electrically disconnectable.
2. Description of Related Art
In recent years, a nonvolatile storage unit for retaining stored information while power is off is a necessary element in a semiconductor apparatus. As such a nonvolatile storage unit, a fuse for irreversibly storing information is known in the art.
The fuse is used to replace a defective memory cell in a semiconductor storage apparatus. The semiconductor memory storage includes a redundant memory cell (redundant circuit) replacing a defect of a memory cell generated in manufacturing process, in order to improve yield ratio. In a test process, the defect of the memory cell is replaced by replacing the defective memory cell with a redundant memory cell. The fuse is used to store information such as an address identifying the defective memory cell.
The fuse stores information according to its connection condition. Thus bad disconnection such as insufficient disconnection causes a misrecognition in the stored information and circuit to be in a malfunction. Without replacing the defective memory cell with the redundant cell, the yield ratio is decreased. As a conventional technique for preventing a malfunction due to a poor connection of the fuse, techniques disclosed in Japanese Unexamined Patent Application Publication No. 3-283196 and Japanese Unexamined Patent Application Publication No. 4-188835 are known.
FIG. 6 is a circuit diagram showing a configuration of a conventional semiconductor apparatus similar to the one disclosed by Japanese Unexamined Patent Application Publication No. 3-283196. In this circuit, laser fuses 601a and 601b are disconnected simultaneously by laser. With either one of the laser fuses 701a to 701c being disconnected, the circuit operates as the fuse is being disconnected.
That is, with the laser fuses 601a and 601a being not disconnected, a current flows from a power supply voltage VDD through a resistance 604, thus a switch 603 is turned off. With either one of the laser fuses 601a or 601a being disconnected, the power supply voltage VDD and the resistance 604 is separated, thus the switch 603 is turned on and an output from an inverter 602 is output to an OUT terminal. Although not shown in the drawings, with the laser fuses 601a and 602b being not disconnected, the OUT terminal becomes floating. Thus depending on an signal of the inverter 602 being output to the OUT terminal or the OUT terminal becoming to be floating, a circuit is required for detecting connection/disconnection condition of the laser fuses 601a and 601b. 
FIG. 7 is a circuit diagram showing a configuration of a conventional semiconductor apparatus similar to the one disclosed by Japanese Unexamined Patent Application Publication No. 4-188835. In this circuit, laser fuses 701a to 701c are connected in parallel. The laser fuses 701a to 701c are disconnected simultaneously by laser. With any one of the laser fuses 701a to 701c being disconnected, the circuit operates as the fuse is being disconnected.
Accordingly with the laser fuses 701a to 701c being not disconnected, a current flows from a power supply voltage VDD through resistances 703a to 703c. Thus low level is output from an NAND circuit 702 to an OUT terminal. With any one of the laser fuses 701a to 701c being disconnected, the power supply voltage VDD and any one of the resistance 703a to 701c is being separated. Thus high level is output from the NAND circuit 702 to the OUT terminal.
However there is a following problem due to the laser fuses that are disconnected by laser used as fuses in Japanese Unexamined Patent Application Publication No. 3-283196 and Japanese Unexamined Patent Application Publication No. 4-188835.
To disconnect the fuse by laser, laser is irradiated in a wafer condition, thus the fuses are disconnected in a wafer test process. At this time, the disconnection by laser needs to be performed by a fuse disconnection apparatus different from a wafer test apparatus. Therefore, after performing the wafer test by the wafer test apparatus to detect a defective memory cell, the wafer needs to be moved to the fuse disconnection apparatus to disconnect the fuses by laser, and then the wafer is tested by the wafer test apparatus that there is no defect in a replacement with a redundant cell. Accordingly more time is required for the test due to the apparatuses to be moved.
Furthermore, the number of fuses to be disconnected by a laser irradiation is limited, and there are various positions of the fuses to be disconnected for each chip. Thus the fuses to be disconnected for all chips over a wafer cannot be disconnected at a time. Accordingly positioning laser and a disconnection need to be repeated for a number of times, thereby increasing time taken for the test due to the disconnection of the fuse.
Because the fuses are disconnected by a laser irradiation, the fuses need to be exposed over a surface of the semiconductor chip. Thus lines cannot be disposed over and below the fuses in a region where an influence from the laser remains. Further, minimum size of the laser fuses is determined by a wavelength of a laser beam. Thus an area occupied by the laser fuses is increasing relatively to areas for other circuits that continue to reduce their sizes. Accordingly with a several dozens or hundreds of fuses formed over a semiconductor chip, the number of components on chip is reduced, creating a large constraint in a reduction of chip size.
There is another problem that in the circuits of FIGS. 6 and 7, a current flows from the power supply voltage VDD to the GND through fuses and resistances with the fuses being connected, thus the current is consumed at any time. It is possible to suppress the consuming current to some extent by appropriately selecting resistance value. However the increase in the consuming current due to non-disconnected fuses can be a huge issue in a circuit requiring several hundreds of fuses.